This invention relates to a programming system for a sewing machine which forms a desired seam on a workpiece by means of varying relative position between the needle and the workpiece according to programmed stitch instructions (this type sewing machine will be called hereunder a program controlled sewing machine). More particularly it relates to a programming system for preparing the above-mentioned stitch instructions according to operation of a manual member operable for varying relative position between a record medium wherein a profile corresponding to the above-mentioned seam is figured and an index member therefor, in such a way that the index member traces the profile.
There have been conventionally proposed many kinds of programming systems for the program controlled sewing machines. One of those programming systems was aimed to consecutively prepare stitch instructions by means of tracing the profile, figured on the record medium, corresponding to the seam, and was provided with a driving mechanism for varying the relative position between the index member and the record medium and a manual member for indicating the direction of variation of the relative position and for making the driving mechanism operate. For example a programming system provided with four keys for the purpose of varying the relative position in both directions of the X axis and the Y axis was known. In this system the driving mechanism varied the relative position between the record medium and the index member in a designated direction by the manual member, and the variation speed of the relative position was set at a constant low speed because exact programming for complicated parts of the profile required setting of the variation speed at a low level.
However, operation of the driving mechanism at the above-mentioned constant low speed was inefficient when the programming was carried out for straight linear or gently curved portions of the profile, and skilled operators desired to do the programming at a higher speed than the already mentioned constant low speed. On the contrary, even the already mentioned constant low speed was too fast to exactly trace the profile when the programming was conducted at extremely complicated parts thereof. Such was an inevitable disadvantage to the prior art.